Verapamil-Sensitive Upper Septal Idiopathic Left Ventricular Tachycardia Prevalence, Mechanism, and Electrophysiological Characteristics

Objectives This study sought to demonstrate the prevalence, mechanism, and electrocardiographic and electrophysiological characteristics of upper septal idiopathic left fascicular ventricular tachycardia (US-ILVT). Background ILVT is classified into left anterior and posterior types with no clear data about US-ILVT. Methods Among 193 ILVT patients, we identified 12 patients (6.2%; age 41 ± 22 years, 7 men) with US-ILVT. Results Of 12 patients with US-ILVT, 6 patients (50%) had previous history of radiofrequency catheter ablation for common ILVT. Sustained VT (cycle length: 349 ± 53 ms) was seen in all patients with a QRS interval slightly wider (104 ± 18 ms) than that during sinus rhythm (90 ± 19 ms). The VT exhibited an identical QRS configuration as sinus rhythm in 6 (50%) and incomplete right bundle branch block configuration in another 6. His-ventricular interval during VT was always shorter than that during sinus rhythm (27 ± 5 ms vs. 47 ± 10 ms). Purkinje potentials were activated in a reverse direction to that of common ILVT; namely, the diastolic potential (P₁) was activated retrogradely but the pre-systolic potential (P₂) was activated antegradely. At the left upper-middle ventricular septum, P₁ potential was recorded during VT, preceding the QRS by 54 ± 20 ms. Radiofrequency catheter ablation at that site eliminated the VT with no recurrence during a 58 ± 35 months of follow-up. Conclusions US-ILVT is an identifiable VT that shares common criteria with ILVT and has a narrow QRS interval. Some US-ILVT cases appeared after common ILVT ablation. It is a reverse type of common ILVT (orthodromic form) with baseline morphological abnormalities that might provide a potential substrate for such VT.